The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
D. S. HARRISON
M. E. MARVEL
ricultural Extension Service Institute of Food and Agricultural Sciences
University of Florida, Gainesville
EQUIPMENT AND METHODS
HOT WATER TREATMENT
OF VEGETABLE SEED
Dalton S. Harrison and Mason E. Marvel1
Some diseases of vegetable crops
are seed-borne. Many seed-borne
diseases are most destructive to
vegetable crops. These diseases
may be carried on the seed, in the
seed, or both. Those carried on the
surface of the seed are more easily
controlled than the ones that are
present inside the seed. The most
effective control for internally-
borne diseases is hot water seed
One of the most important in-
ternally-borne diseases of vege-
table crops in Florida is black rot
of crucifers, caused by a bacterium
(Xanthomonas campestris). Some
seasons cabbage and related crops
are severely attacked, and in cer-
tain instances one hundred percent
infection of cabbage fields has oc-
curred. Even a few infected plants
in a field may lead to spread of the
disease by wind, splashing rain,
cultivating equipment, i n s e c t s,
man, animals and other means.
Spread is most rapid during
periods with warm days and cool
nights or when frequent rains,
fogs and heavy dews occur.
Controls for black rot include
use of disease-free seed, hot water
seed treatment, crop rotation, and
disease-free plants. It is recom-
mended that all seed of crucifers
be hot water treated because it is
difficult to determine if seed are
disease free. Hot water is also ef-
fective against two other seed-
borne diseases of crucifers,
alternaria leaf spot and blackleg.
Seed of many vegetable crops
may be hot water treated to control
certain seed-borne diseases. Some
of these are:
Celery & Parsley
Black Rot & Blackleg
'Associate Agricultural Engineer and Associate Vegetable Crops Specialist, respectively, Agricultural
Extension Service, University of Florida, Gainesville.
The seed should be immersed in
cool water immediately after treat-
ment, and then spread on trays and
dried before delivery to growers
for planting. In the Hastings and
Belle Glade areas where there are
commercial hot water seed treating
operations, some growers have the
seed dried only enough to prevent
them from sticking together in the
planter. This requires approxi-
mately 12 hours drying time, using
unheated air. It is reported that
this procedure results in quicker
and better germination. Treated
seed, to be kept more than one day
before planting, should be
thoroughly dried (usually 24-36
hours) to prevent sprouting and
Research results indicate that
one year old cabbage, pepper,
celery and eggplant seed may be
hot water treated at the recom-
mended temperature and time and
kept for one year without signifi-
cant reduction in germination.
Seed from recent harvest should
be used. Old seed or weak seed,
that would normally germinate
well enough to be used, may be
damaged by hot water treatment.
Hot water treatment does not
take the place of chemical treat-
ments which control soil-borne in-
sects and diseases. Chemical seed
treatment with recommended
fungicides and insecticides should
be done following hot water treat-
ment after the seeds are dried. Hot
water treated seeds are more sus-
ceptible to soil-borne fungi and
bacteria than untreated seeds when
planted in untreated soil.
rig. -a. Hot water treatment station now operat-
ing in the Belle Glade area. This unit was con-
structed from the plans described in this circular.
For additional information, con-
tact your co u n t y agricultural
The following publications are
Extension Circular 193F. "Com-
mercial Vegetable Insect and Dis-
ease Control Guide."
Experiment Station Circular
S-4. "Cabbage Black Rot and Yel-
lows and Their Control."
Experiment S t a t i o n Bulletin
492. "Diseases, Deficiencies and
Injuries of Cabbage and Other
Crucifers in Florida."
Florida S t a t e Horticultural
Society Proceedings Volume 76.
"Hot Water and Aerated Stream
Treatment of Vegetable Seed."
The inner tank is constructed of
1/-inch sheet iron while the outer
tank is constructed of plywood.
(See Figs. 1, 2 and 3 for details.)
A removable false bottom in the
inner tank is made from wooden
slats (see Fig. 1).
Two 240-volt, 4,000-Watt im-
mersion heaters are mounted one
in each end of the tank, 4 inches
from the bottom of the inner tank.
These are controlled by an immer-
sion thermostat (1/2 to 1F. dif-
ferential) operating the holding
coils of a 240-volt, 2-pole 50-amp
contactor. A .005 MFD condenser
across the contact of the thermo-
switch is recommended when the
thermoswitch is operating the
holding coil of a 230-volt magnetic
contactor. (Fig. 4 and 6).
In the line between the magnet-
ic contactor and the two immer-
sion heaters, a 3-heat switch is
installed. This arrangement, as
shown in Fig. 6 schematic, gives
either 8,000, 6,000 or 2,000 Watts
by, series-parallel connections with
the immersion heaters. A stan-
dardized thermometer is used to
check the temperature. An electric
timer-alarm clock combination, ac-
curate to the minute, is useful in
timing the treatment.
Water is circulated in the tank
by a 300 GPH centrifugal pump,
with 3/4-inch suction and discharge.
This helps maintain a more uni-
form temperature throughout the
tank. A drain pipe is installed in
the bottom of the tank which can
also be used in combination with
a pipe "T" and globe valve for re-
filling. An overflow pipe is in-
stalled 4 inches from the top,
centrally located in one end of the
The seed treatment tank, as con-
structed and described above, will
hold 110 gallons of water when
filled to within 8 inches of the top.
There are demonstration models
(Fig. 1-a) now in commercial use
in Florida, that will bring water
from 800F. to the desired tempera-
ture of 122 F. in 95 minutes. When
the initial temperature is 700F.,
the time required to bring the
water to 1220F. is 115 minutes.
The seed treatment tank has a
capacity of 100 pounds of seed.
Seed should be treated in 50-
pound unbleached muslin bags, 10
pounds to the bag. A large gal-
vanized tub filled with cool water
may be used to cool the seed after
treatment. The bags of treated
seed are cooled and hung on a rack
to drain about 5 minutes before
they are emptied in the trays. A
work table 4 feet wide x 8 feet long
x 3 feet high may be used to hold
the trays while they are being
filled and unloaded.
A seed drying cabinet with doors,
shown in Fig. 5, is built in 3 sec-
tions to contain 48 trays, 2 x 3
feet. Each tray holds 2 to 3 pounds
of seed. Tray bottoms are made of
fine mesh galvanized screen wire.
The doors are closed after the trays
have been filled for drying. An ex-
haust fan 2,000 CFM @ 1/8-inch
S.P. is mounted on top of the dry-
ing cabinet which pulls air through
the trays from the open base (Fig.
5)., Capacity of the drier is 100 to
144 pounds of seed every 24 hours.
The capacity of the drier deter-
mines the capacity of the overall
unit. (The seed treatment unit is
completely automatic and holds the
temperatures within 1/2 degree F.)
Total cost of the unit is approxi-
mately $850. Costs of the unit
described are listed in the appendix.
1. Fill tank with water, to within 8-inches of top (this requires 110
gallons of water).
2. Turn Main Switch on.
3. Turn 3-Heat switch to "High" position. (When the water has an
initial temperature of 800F, the time required to raise to 122F is
approximately 95 minutes. If the initial temperature is 750F, the
time required to raise to 1220F is 105 minutes.)
4. Turn circulating pump switch "on".
5. When the tank has reached the desired temperature and the mag-
netic contactor has disengaged the heaters, the 3-Heat switch may
then be turned to the "Medium" position for holding the temperature
while seed is being treated. The "Low" position is used to hold the
water at the desired temperature when there is a lapse of one hour
or more between seed treatments.
6. The unit is now ready for treating seed.
7. When it is desired to change the thermoswitch to other temperature
settings, remove the cover and adjust with small screwdriver.
SEED DRYING CABINET
The shell of the cabinet should be made of /4" plywood.
The doors should be /8" plywood.
Part Material & Size
Two Sides 2 Sheets 4' x 8'
Back 2 Sheets 4' x 8'
Doors Bottom 2 Sheets 4' x 8'
1 Sheet 4' x 8'
2" x 2" Vertical Support 30 ft. 2" x 2" .12/lin. ft.
1" x 2" Horizontal Support 368 ft. 1" x 2" .06/lin. ft.
1" x 3" Trays 480 ft. 1" x 3" .11/bd. ft.
2" x 4" Legs 12 ft. 2" x 4" .12/bd. ft.
APPROXIMATE COST .......----......--.... $100.00
LIST OF EQUIPMENT USED FOR
DEMONSTRATION MODEL UNIT
1 ea. Chromalox Type SS 3 heat AC snap switch, #SS-9772-5,
250V., 8750 Watts, incl. conduit box and cover ---........-... $15.00
1 ea. L. R. H. Labaw 300 GPH 3/4" centrifugal pump and 1/4 h.p.
motor ..............................----...--.....--........-- ---$25.00
2 ea. Chromalox Type ARMT, 240V, Ip, 4000 Watt, 2" Std.
Screw plug, copper sheath, Immersion heaters ..........- ..... $140.00
1 ea. 60 amp. fused disconnect ...-.----... ---.........------.- $20.00
1 ea. 2,000 CFM @ 1/8" s.p. Exhaust fan w/11OV. Motor ...----$60.00
1 ea. Chromalox Type k-250, 50 amp., 2-pole Ac, 240 Volt Mag-
netic Contactor .......--.......-- ---.................-.... $80.00
1 ea. Fenwall, Series 17800 immersion Junction box type ther-
moswitch unit (1/2 to 10 diff.) ........................-- ....---..$25.00
Misc. Elec. fittings and supplies .......... ........ ..... ............. $40.00
Approx Total Cost for Equipment -.............. $405.00
Approx Total Cost for Drying Cabinet ..-........-..... 100.00
Approx Total Cost for Treatment Tank ..---- .----- 125.00
Approx Labor .......... ---------------...................... 200.00
(Trade or Brand names does not indicate Extension Service endorse-
ment, but rather to identify those used on demonstration model).
BILL OF MATERIALS
HOT WATER TREATMENT TANK
All plywood to be
Long & Short Sides
Bottom & Top
/8" exterior marine plywood.
2 Sheets 4' x 8'
2 Sheets 4' x 8'
To be made of 1/8" sheet iron.
Long & Short Sides
Metal Plates on Legs Use left over
All of Angle Iron Frame
Bottom Support for Tank
1 Sheet 4' x 8'
1 Piece 2' x 4'
from 4' x 8' sheet
2" x 2" x 3/16" x 48 ft.
1" x 22" Channel
Styrofoam insulation to be used.
Long Sides 2 Sheets 521/2" x 32" x 2"
Short Sides 2 Sheets 251/2" x 32" x 2"
Bottom 1 Sheet 481/" x 241/2" x 2"
Top 1 Sheet 455,/" x 215/8" x 2"
Total Board Feet -.....--...................... 100 bd. ft.
APPROXIMATE COST ..............----- .......--- $125.00
FIGURE I. SEED TREATMENT UNIT
FIGURE 2. ANGLE IRON FRAME FOR INNER TANK
FIGURE 3. ISOMETRIC OF INNER AND OUTER TANK.
^ ^-^ ll, \^ ^
FIGURE 4. MLCI-ANICL AWD LLECTRICAL LQUIPME.T.
~ l ,E: x,
2 x35 TDAYS
I", 3" LUMPLR
F PRONT VIEW
- II -
- II II -
__ 1 II -
-- I -II-
VIEW WITH DOORS OPEN
FIGURE 5. SELLD- DYING CABINET.
L I -.
G ~SCALAIA TIC DIkG
(REV-tD 10/91/ (1)
RQA ok F E L ECT RfIC .L- t h T I WG
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida
Florida State University and United States Department of Agriculture, Cooperating
M. O. Watkins, Director